Oxygen process



H. J. OGORZALY OXYGEN PROCESS Filed Oct. 12, 1946 Hairy J. ogorzals' Sink/ember Patented July 10, 1951 2,560,469 oxvenn rnocuss Henry J.

ration of Delaware Ogorzaly, Summit, N. J., Standard Oil Develop assignor to ment Company, a corpo- Application October 12, 1946, Serial No. 703,000

8 Claims. (Cl. 62-175.5)

The present invention is concerned with an improved process for the production of oxygen from air. The invention is more particularly concerned with an arrangement and sequence of heat exchanging stages by which improved efficiency in the exchange of heat is secured. In accordance with the present process at least one solid heat exchange medium is circulated between the incoming feed air stream and the outgoing product stream under conditions to secure direct Contact between the circulating heat exchange medium and the air stream and the product stream. The preferred modification of the present invention'comprises employing a plurality of heat exchange'mediums, one of which comprises solid materials, for transferring refrigeration from the product stream to the feed air stream and simultaneously controlling the critical temperature range over which the particular selected medium is used.

By operating in accordance with the present invention' unexpected desirable results are secured and the efliciency of the operation is materially improved.

It is well known in the art to manufacture oxygen and nitrogen from air. In these processes, the air is liquefied and fractionated to secure products having the desired high quality and purity. Since the operation is conducted at very low temperatures, it is obvious that one major problem encountered is the efiicient transfer of refrigeration from one stream to the other. Various proposals and suggestions have been made for the eificient transfer of heat from the incoming air stream to the chilled outgoing product streams. In the design of suitable heat exchange equipment, the problem is complicated by the fact that in cooling air to the desired temperature, water vapor freezes out in the form of ice, and carbon dioxide in the form of carbon dioxide snow. Thus, in a relatively short period of time the heat exchange equipment is plugged due to the ice and carbon dioxide snow.

One process that is currently used to overcome the plugging of exchangers or accumulators is to use reversible exchangers or accumulators. In

this process the incoming air stream is com-- pressed to a pressure in the range from about 4 to about 8 atmospheres and higher and is caused to exchange heat countercurrently against the outgoing cold product streams. The cold product streams are usually at lower pressures, generally around atmospheric pressure. After the streams have flowed through their respective channels for a period of time, and the ice and snow plugging in the air channel has not as yet reached a critical maximum, the flow paths of the respective streams are switched. That is, the cold product streams are caused to flow through the paths previously employed by the warm incoming air, while the air employs the passageways previously used by the product gases. The direction of flow of the gaseous streams is not changed. As a result of this reversal, the carbon dioxide and the water vapor deposited fromthe air in the previous half cycle are caused to revaporize or sublimate into the lower pressure product streams and they are then carried out with the product gases.

Since the outgoing nitrogen and oxygen product streams are colder than the chilled air stream from which the ice and carbon dioxide is condensed, the success of the reversible exchanger depends upon a balance of the differences in the respective temperatures and pressures. If carbon dioxide snow is to be revaporized there exists a critical maximum temperature difierence which must not be exceeded, otherwise sublimation of the carbon dioxide snow will not be secured even at the lower pressure of the reversing streams.

I have now discovered an improved process for transferring refrigeration from the chilled .product streams to the incoming feed air streams. In accordance with my invention, I utilize at least one solid heat transfer medium to transfer refrigeration between the respective streams in an efiicient manner. The process of my invention may be readily understood by reference to the attached drawing illustrating an adaptation of the same.

The incoming feed air stream is introduced into the system by means of line I. The feed air stream is introduced into centrifugal compressors Pl or equivalent means. Compressors Pl may include intercoolers and are preferably driven by a condensing steam turbine. The feed air stream is compressed to 5 atmospheres gauge, withdrawn from compressors P-I by means of line 2 and passed to after-cooler E-l in whichthe air stream is cooled to a temperature of about F. Water is introduced into aftercooler EI by means of line 3 and withdrawn by means of line 4. The compressed air is introduced into the top of water removing zone 6 by means of line 5. The condensed water is removed in zone 6 and collects in the bottom thereof. A portion of the condensed water is withdrawn by means of line 1 and used as make-up water in the circulating brine solution hereinafter described. Any remaining or excess water is removed from the system by means of line 8. The compressed air is removed overhead from zone 6 by means of line 9 and introduced into the bottom of air-brine contacting zone Tl through a distributing head or manifold 10. The air flows upwardly through zone Tl and is cooled to a temperature of about 10 F. by downflowing calcium chloride brine which is introduced into the upper part of zone T-| by means of line I I. The brine is introduced at a temperature of about -l7 F. and withdrawn by means of line I 2 at a temperature of about 98 F.

Air brine contacting zone T-I may comprise any suitable type of equipment. Zone T-l may contain wooden grids G-I, G-2, G-3 and G--4 or equivalent means as packing to secure eflicient contact between the counterfiowing streams. Zone T-l may likewise contain adequate distributing troughs and the like.

The air stream cooled at a temperature of 10 F. is drawn overhead from zone T-l by means of line l3 and introduced into ammonia chilling zones E--2a and E--2b by means of lines I and I5 respectively. The ammonia chilling zones or equivalent means are designed to cool the air at a pressure of 5 atmospheres (gauge) from about F. to about -30 F. The air is maintained on the tube side while the ammonia is maintained on the shell side of the exchanger. The air in the tube side is periodically replaced with nitrogen gas in order to remove ice which condenses out from the air on the tube side and avoid plugging of the tubes.

Ammonia liquid is introduced into zones E2a and E2b by-means of lines l6 and I! respectively. The ammonia boils at about -40 F. at a pressure of 10.4 pounds per square inch absolute on (the shell side and is removed from zones E2a and E2b by means of lines l8 and I9 respectively.

Air at a temperature of about 10 F. is introduced into zone E-2a by means of line l4 and withdrawn from zone E2a by means of line at a temperature of 30 F. During this cycle nitrogen is introduced into the tube side of exchanger E2b at a temperature of about -32 F. by means of line 2|. The nitrogen is withdrawn from exchanger EZb by means of line 22 at a temperature of 33 F. and introduced into the bottom of nitrogen brine contacting zone T2 hereinafter described.

On the other half of the cycle, air is introduced into zone E2b by means of lines l3 and I5 and withdrawn from zone E2b by means of line 23. During this cycle nitrogen is introduced into the tube side of zone E2a by means of line 24, withdrawn by means of line and likewise introduced into the bottom of zone T2.

Zones E2a and E-2b with their accompanying feed and withdrawal lines for ammonia, nitrogen and air, are properly equipped with a suitable valve arrangement so that the above described cycle may be secured. It is to be understood that it is within the scope of my process to operate zones EZa and E2b in parallel for at least a portion of the time and only to pass nitrogen through the tubes for a sufficient length of time to keep the tubes from plugging.

In accordance with my invention, the air withdrawn from zones EZa and E2b is introduced into the bottom of an air-solid contacting zone T-4. For the purpose of illustration, in accordance with a preferred modification of my invention, the solids comprise lead pellets. It is to be understood that other solids, as for example metallic silver, calcium, zinc or salts such as silver iodide, may be employed. In general, the use of solids other than lead will require more than one stage of direct contact between the solid and the gases to efiect the transfer of heat over the same range of temperature. The air is introduced into the bottom of zone Tl by means of distributing lines 26. The air flows upwardly through the interstices of a bed of downward flowing lead pellets 21. Air at a temperature of about -275 F. is withdrawn from the top of zone T4 by means of line 28. Air lead contacting zone T4 is operated at a pressure of about 73 pounds per square inch gauge pressure. The lead pellets are introduced at a temperature of about 285 F. and are withdrawn at a temperature of about 31 F. Although the depth of the bed may vary, it is preferred for example, that when the cross-sectional area of zone T-4 is about 226 square feet and the equivalent diameter about 17 feet with the height of the sides around 13 feet, the depth of the lead pellet bed should be about 8 feet.

The chilled air at a temperature of about 275 F. is introduced into the bottom of high pressure fractionating tower TB. This tower is operated at a pressure of about '72 pounds per square inch gauge and between the temperature limits of from about -280 F. to 287 F. This high pressure tower comprises suitable fractionating plates. Substantially pure nitrogen is removed as an overhead vapor stream from the high pressure tower by means of line 29 at a temperature of about -286.5 F. while the bottoms stream comprising an oxygen-rich liquid stream containing from about 40% to about 50% of oxygen is removed by means of line 30 at a temperature of about 280 F. From the bottom of high pressure fractionating zone T8, I withdraw a slurry comprising solid carbon dioxide by means of line 3| at a temperature of about 280 F. This slurry is circulated by means of centrifugal pump P2 through carbon dioxide filter zone V2 in which the solidified carbon dioxide is removed. The bottoms slurry stream from which carbon dioxide is removed is introduced into line 30 by means of line 32 and handled as hereinafter described. A portion of the slurry recirculated by pump P2 is not passed through filter zone V2, but is introduced into the top of a scrubbing section of high pressure fractionating tower T-8 by means of line 33. This portion of the slurry counter-currently contacts the upflowing air stream introduced into the bottom of zone T8 and removes therefrom carbon dioxide snow and other solids. Carbon dioxide filter zone V2 may be equipped to be blown through with cold compressed air and to flush out the carbon dioxide deposit with a purge stream of nitrogen at intervals.

The oxygen-nitrogen stream comprising about 45% oxygen and 55% nitrogen at a pressure of about 70 pounds per square inch is passed to a high pressure tower bottoms cooler zone E3. In exchanging zone E3 the liquid oxygen-nitrogen stream is cooled from a temperature of about 280 F. to a temperature of about 289 F. This cooled oxygen-nitrogen stream is withdrawn from zone E3 by means of line 34 and introduced into an intermediate point of low pressure fractionating tower T9. Liquid nitrogen at a temperature of about -306 F. is introduced into zone 5-3 by means of line 35 and withdrawn from zone 51-3 at a temperature ofabout 284" F. by means of line 38.

The liquid feed stream introduced into zone T& by means of line 34 flows downwardly in the low pressure tower through the stripping section in which it is freed of nitrogen by contact with vapors rising from the reboiler section in the bottom of the tower. The nitrogen-free liquid stream is vaporized in the reboiler section and a part of the vapor is returned up the tower while another part is withdrawn as oxygen product from low pressure tower T9 by means of line 38 at a-temperature of 292 F. The heat supplied to the bottom of low pressure tower T! is maintained by condensing the major part of the nitrogen leaving the high pressure tower T-B through line 29. A part of the condensed nitrogen is returned by means of line 35 to provide reflux in high pressure tower T-8 while. another part is introduced into the top of low pressure tower T9 by means of line ll through throttling valve 50. Prior to introducing this reflux nitrogen into the top of low pressure tower T--9 it is passed through a reflux nitrogen cooler E-J. In this zone liquefied nitrogen is cooled at '10 pounds per square inch from its boiling point of 286.5 F. to 300? F. with vapor nitrogen at about 3 pounds per square inch gauge pressure and at a temperature of 315" F. to about 306" F. The vapor nitrogen is introduced into zone E-l by means of line 42 and withdrawn by means of line 35. 'Low pressure tower T9 is operated at a pressure of about 3.5 pounds per square inch under conditions to withdraw overhead by means of line 31 a pure vaporous nitrogen stream at about 315" F.

A portion of the nitrogen stream removed overhead from high pressure tower T8 by means of line 29, the major part of which is passed to the condenser-reboiler in the bottom of zone T-S, flows to nitrogen expander surge drum V-3 by means of lines 43 and 44. Prior to introducing this stream intozone V--3, it is mixed with a small stream of nitrogen at a temperature of about 35" F. which is introduced by means of line 45. The relative quantities employed are sufiicient to secure a temperature of at least 256 F. at a pressure of 72 pounds per square inch in the lower half of zone V-3.

The warmed nitrogen stream is withdrawn from the lower half of zone V3 by means of line 46 at a temperature of at least 256 F. and at a pressure of about 72 pounds per square inch gauge, passed to centrifugal expansion engine P-3 and then discharged into the upper half of zone V3 at a temperature of about 315 F. and at a pressure of about 5 pounds per square inch by means of line 41. The cool vapors are withdrawn from the top of zone V3 by means of line 42 and handled as hereinbefore described. A suflicient quantity of nitrogen withdrawn from the top of zone T-B by means of line 28 is. passed through expander nitrogen-lead contacting zone T'!, in order to warm it from about 286.5 F. to about 35 F. This is accomplished by means of lines and 48.

The lead pellets are withdrawn from air-lead contacting zone T-l by means of line 50 at a temperature of about 31 /2 F. and under pressure of about 72 pounds per square inch gauge. These lead pellets comprise pellets having a diameter of approximately These pellets are moved under pressure through bucket conveyor arrangement 50 or similar means and various portions of them passed into lead pellets accumulator zones V-4. V-t and V-B. Lead accumulator zone V-4 is anaccumulator zone for the nitrogen tower, while lead accumulator zone V-li is a lead accumulator for the oxygen tower, and lead accumulator zone V6 is a warm lead accumulator for the expander nitrogen tower.

The lead pellets from the lead accumulator zone 7-4 are passed into the lock hopper feed zone for the nitrogen tower V|. In zone VI the pressure on the pellets is reduced from about '12 pounds per square inch gauge to the low pressure of about 2 pounds per square inch gauge at which nitrogen-lead contacting zone T5 operates. These lead pellets are passed through a suitable valve arrangement from zone V-I into the productnitrogen-lead contacting zone T-5. In this zone the lead pellets form a bed 5| in the bottom area thereof. Product nitrogen withdrawn from zone E-3 by means of line 36 is introduced into zone T5 by means of distributing lines 52. This product nitrogen flows upwardly between the interstices of the lead pellets of bed 5| and is withdrawn from the upper part of zone T--5 by means of line 2|.

The product nitrogen flows through zones E2a and E-2b as previously described, and is then introduced into nitrogen brine contactor T-! by means of line 53. A portion of the nitrogen may by-pass zones E-2a and E2b by means of line 54. The product nitrogen flows upwardly through zone T-Z and countercurrently contacts downflowing brine which is in troduced intothe upper part of zone T2 by means of line l2. The product nitrogen is vented overhead from zone T-2 into the atmosphere, or it may be collected and used in any manner desirable. Nitrogen brine contacting zone T-Z may contain any suitable packing or distributing means.

The lead pellets are withdrawn from zone T5 by line or conveying means and introduced into lock hopper feeding zone V-IU. In this zone the pressure by proper control of the respective valves is increased from the pressure existing in zone T5 of about 2 pounds gauge to the pressure existing in zone T-4 of about 73 pounds per square inch.

The lead pellets introduced into zone V5 which comprises the lead accumulator zone for the oxygen tower are then passed into zone V--8 which comprises the lock hopper feeding into low pressure product oxygen-lead contacting zone T-G. The lead pellets form a bed in the lower area of zone T-6. Product oxygen withdrawn from lowpressure fractionating zone T& by means of line 38 is introduced into zone T-B by means of distributor lines 8|. The product oxygen flows upwardly through bed 60 and is withdrawn from the upper area by means of line 62.

This product oxygen is then passed into the lower section of oxygen brine contacting zone T-I. The product oxygen flows upwardly through zone T-3 and countercurrently makes heat exchange with the down-flowing brine which is introduced into the top of zone T-3 by means of line 63. Product oxygen is removed overhead from zone T-3 by means of line 54 and handled in any manner desirable. Lead pellets are removed from zone T-6 by means of conduit or conveying means 64 and handled in a manner similar to that described with respect to the pellets by means of line 55.

Lead pellets passed into zone V--6 are passed into cold lead accumulator zone T-T which operates under pressure of about 72 pounds per square inch gauge. In this zone the lead pellets contact. as heretofore described, nitrogen which is introduced into zone V9 by means of line 48 and withdrawn by means of line 45. The lead pellets are withdrawn from zone T--'l and introduced into cold lead accumulator V-9 which acts as a feed hopper to zone T4. The

lead pellets are passed from zone V-9 to zone T-4 by means of line 10 and handled as heretofore described.

My invention is generally concerned with an improved oxygen product process wherein oxygen is separated from air by a liquefaction-fractionation process in which a major part of the heat transferred from cold product gases to relatively warmer entering air is effected by means of a circulation of solid lead particles. In general, the process comprises compressing air to 5 atmospheres gauge and cooling to about 100 with water. The air is then cooled with a calcium chloride brine solution or an equivalent solution in a tower preferably packed with vertical wood grids in order to cool the temperature to about -l0 F. In a second air cooling stage, the air is further chilled with ammonia or an equivalent cooling medium to about 30 F. The air is withdrawn from the second cooling stage and in accordance with my process is passed through a bed in which the heat is transferred from the outgoing product streams to the incoming air stream in the tertiary cooling stage by means of a solid cooling transfer medium. The preferred method of operating is to employ a moving bed of solid heat transfer medium which comprises metallic spheres, as for example lead spheres. The diameter of the spheres may vary in the range from about A;" to 1" and higher. It is preferred that the diameter of the spheres be in the range from about to in diameter.

In the tertiary cooling stage, the air is chilled to a temperature of about 275 F. The chilled air which is close to a saturation point is introduced into the bottom of a high pressure fractionating tower operating at a few pounds below 5 atmospheres gauge where it is first subjected to a scrubbing action with a pump-around slurry stream for the purpose of removing carbon dioxide snow carried in the gas. A portion of the slurry is passed through a sand filter or equivalent means, preferably provided in duplicate from which the carbon dioxide is periodically vaporized in amounts equivalent to the rate of introduction in the air feed.

The air fractionating system comprises a low pressure tower operating at a few pounds per square inch above atmospheric pressure and a high pressure tower which operates as described heretofore.

Additional refrigeration is obtained by the expansion in a work engine of approximately 13% of the nitrogen product, which is available as gaseous vent from the high pressure tower. The cold returning products leaving the fractionation system in gaseous form are used first to chill the 4'' lead pellets to -285 F. before these pellets are employed to cool the incoming air. A small side stream flow of lead is also employed to warm the portion of the nitrogen entering the expansion engine, in order to avoid condensation within the engine. The separated products leave the lead contacting towers at 32 F. and are used to chill the circulating brine solution prior to its contact with the warm compressed air. The contact of the brine with these low pressure gases results in a net vaporization loss of water which is balanced by introducing a portion of the water in the compressed air.

By far the major part of the water in the entering air stream is removed in the compressor aftercooler and the brine contact tower. A residual is deposited in the ammonia chillers. These are accordingly provided in duplicate with nitrogen gas at low pressure returning through the tubes of the unit not employed in chilling air. The deposited ice is thus sublimated into the low pressure returning stream. Automatic switching of the flows at intervals is provided. A remaining small proportion of water is carried further into the lead circulation system and is transferred by the lead from its point of deposition in the air tower to the product towers where it is vaporized.

The CO2 content of the air is substantially all deposited as a solid in the lead contacting tower. Since the temperature at the bottom of this tower is too high to permit the retention of CO2 solid on the spheres leaving the tower, the upper portion of the tower fills with CO: snow. This is sufl'iciently dry in nature so that it is carried overhead in the chilled gas, to be removed in the slurry scrubbing system and sand filter provided in the fractionation section.

In a designed system, the lead circulation system requires the transfer of approximately 43 tons per minute of lead to a vertical height of feet and its separation into two major and one small stream. Because of the pressure differentials existing between the air and product streams, lock hoppers are provided to effect pressure seals between these streams. Automatically operated valves in this cycle operate at a one minute interval between changes in position.

The essential novelty of this process resides in the storage of refrigeration in the circulating solid and its bodily transport within the solid to a zone where it can be utilized. Metallic lead is the most satisfactory solid, but other materials which may be used for a solid heat transfer medium comprise tellurium, silver, calcium, zinc, potassium bromide, silver iodide and the like. Except for its rarity, tellurium is equally as satisfactory as lead for use in air separation plants. All other solids, however, are less satisfactory in that their heat capacity varies to a greater extent with change in temperature level in the refrigerating zone. In adiabatic interchange of heat between solids and cold gases, which maintain substantially constant heat capacity, appreciable temperature separation between the solid and the gas occurs as a consequence of the variation in heat capacity of the solid at different tempera ture levels. When the solid is utilized for transferring heat between two gases, a differential temperature separation from either gas in excess of the total differential between the two gases cannot be tolerated. As a result, a single-stage of gas-solid contacting can only be used to transfer heat between two gases over a limited range of temperature which is defined by the variation in heat capacity of the solid with temperature level and by the magnitude of the temperature differential between the two gases. The allowable range of temperature is greatest with lead among common metals, followed by silver, calcium, and zinc. Silver iodide and potassium bromide are among the better salts. In many applications of heat transfer by direct countercurrent contact of gas with moving solid, this factor is of minor importance; but when the differential temperaing must be introduced in order to reduce the temperature range to within the limits established by the characteristics of the solid employed.

The process of my invention is not to be limited by any theory as to mode of operation, but only in and by the following claims in which it is desired to claim all novelty insofar as the prior art permits.

I claim:

1. In a process for the manufacture of nitrogen and oxygen gas from air and wherein liquid air is fractionated to produce a cold oxygen and a cold nitrogen stream, the improvement which comprises employing 3 successive cooling stages for an incoming air stream to be fractionated, cooling the previously cooled incoming air stream in the third and coldest zone by directly contacting the chilled gaseous product streams in a countercurrent manner with a moving solid transfer medium, whereby said solid transfer medium is chilled and said product streams are warmed, then contacting the said previously cooled incoming air stream with said chilled moving solid heat transfer medium moving countercurrently, the said previously cooled incoming air stream and to warm the solid heat transfer medium and recycling said warm solid heat transfer medium to said product streams.

2. Process as defined by claim 1 wherein said solid medium comprises metallic spheres having a diameter in the range fromabout ,4 to about 3. Process as defined by claim 1 wherein said.

solid medium comprises lead spheres.

4. In a process for the manufacture of nitrogen and oxygen gas from air and wherein liquid air is fractionated to produce a cold oxygen and cold nitrogen stream the improvement which comprises, cooling the air from a temperature in the range from about 90 F. to 110 F. to a temperature in the range from about 5 F. to F. by circulating in direct heat exchange therewith a calcium chloride brine solution, which solution is also circulated in direct heat exchange with the nitrogen and oxygen products streams, passing the chilled air to a second cooling stage wherein the air is cooled in temperature from about 5 F. to 15 F. to a temperature in the range from about 25 F. to -35 F. by being in indirect'heat exchange with a refrigerant medium, passing the chilled air to a tertiary stage wherein the air is cooled from about -25 F. to about 35 F. to a temperature in the range of about -272 F. to --275 F. by being in direct heat exchange with a solid heat exchange medium, said solid heat exchange medium being circulated and in direct contact with the nitrogen and oxygen product streams.

5. Process as defined by claim 4 wherein said solid medium comprises metallic spheres.

6. Process as defined by claim 4 wherein said solid medium comprises lead spheres having a diameter in the range from about A" to about 3/1"- 7. In the process for the manufacture of nitrogen and oxygen gas from air wherein air is liquefied and thereafter fractionated to separately obtain oxygen and nitrogen, the improvement which comprises subjecting air to a preliminary cooling by heat exchange with a cold brine solution, cooling the said brine solution by heat exchange with cold gaseous streams of nitrogen and oxygen, respectively, charging the thus cooled air to a second cooling stage where it is further cooled by heat exchange with a refrigerant, withdrawing the thus further cooled air from the said second stage, charging it to a third stage where it is cooled to a temperature as low as about 275 F. by contacting it with a solid heat transfer medium and cooling the said solid heat exchange medium by direct contact with the nitrogen and oxygen streams proceeding from the fractionattijon prior to contacting the air in the said third s age.

8. The method of producing oxygen by the liquefaction and rectification of air, which comprises passing downwardly through one zone a mass of pellets, flowing upwardly through said zone in contact with said pellets and substantially uniformly distributed therethroughout a stream of rectification product, withdrawing said pellets from the base of said zone at a temperature close to that of the incoming rectification product stream, passing the withdrawn chilled pellets downwardly through a second zone countercurrent to a rising stream of air substantially uniformly distributed throughout the pellets flowing through 'said second zone, withdrawing the air from said second zone at a temperature close to that of the incoming pellets and withdrawing the pellets from said second zone and reintroducing them into the top of said first mentioned zone.

- HENRY J. OGORZALY.

REFERENCES CITED 'The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,178,667 Niewerth Apr. 11, 1916 1,871,166 Fahrbach Aug. 9, 1932 FOREIGN PATENTS Number Country Date 525,197 Great Britain Aug. 23, 1940 

8. THE METHOD OF PRODUCING OXYGEN BY THE LIQUEFACTION AND RECTIFICATION OF AIR, WHICH COMPRISES PASSING DOWNWARDLY THROUGH ONE ZONE A MASS OF PELLETS, FLOWING UPWARDLY THROUGH SAID ZONE IN CONTACT WITH SAID PELLETS AND SUBSTANTIALLY UNIFORMYL DISTRIBUTED THERETHROUGHOUT A STREAM OF RECTIFICATION PRODUCT, WITHDRAWING SAID PELLETS FROM THE BASE OF SAID ZONE AT A TEMPERATURE CLOSE TO THAT OF THE INCOMING RECTIFICATION PRODCUT STREAM, PASSING THE WITHDRAWN CHILLED PELLETS DOWNWARDLY THROUGH A SECOND ZONE COUNTERCURRENT TO A RISING STREAM OF AIR SUBSTANTIALLY UNIFORMYL DISTRIBUTED THROUGHOUT THE PELLETS FLOWING THROUGH SAID SECOND ZONE, WITHDRAWING THE AIR FROM SAID SECOND ZONE AT A TEMPERATURE CLOSE TO THAT OF THE INCOMING PELLETS AND WITH DRAWING THE PELLETS FORM SAID SECOND ZONE AND REINTRODUCING THEM INTO THE TOP OF SAID FIRST MENTIONED ZONE. 